Negreanu was born in Toronto, Ontario. In 1974, his parents, Annie and Constantin, emigrated from Romania, hoping to start a new life in the United States. Instead, they ended up settling in Toronto, where Constantin worked as an electrician and sold confectionery. Daniel was born five years after his brother, and even at an early age was extremely ambitious. "From the age of four, I thought I’d be rich. I told my mom I’d build a house out of Popsicle sticks, and move to California," Daniel recalls in a 2009 interview.[6]

He attended Pineway public middle school in North York, where the principal complained to his mother about Daniel's "poor manners or behavior" and threatened to expel him for "ignoring the school rules."[6] While nursing dreams of a career as a professional snooker player, the then 15-year-old learned how to play poker. By 16, he was spending time in pool halls, hustling, sports betting, and playing cards.[7]

When he was several credits short of graduation, he dropped out of high school and began his life as a rounder playing at the local charity casinos, usually at Casino Country and Fundtime Games, and looking for illegal games around the city.[7] While in Toronto, he met and began dating Evelyn Ng,[8] who would also become a well-known professional poker player. After building up his bankroll, he left for Las Vegas at the age of 22 to pursue his dream of becoming a professional poker player. However, "The Strip" got the better of him and he was forced to move back home to Toronto to rebuild his bankroll.

In August 2005, he married Lori Lin Weber; they separated in November 2007.[9]

Negreanu has a blog at Full Contact Poker where he posts his thoughts and feelings about life, politics, and the poker world. He is also a heavy National Hockey League (NHL) fan, once claiming on Poker After Dark at the dream table he was thinking of declining the offer because the tournament was in the middle of hockey season. He is often seen wearing NHL jerseys of the Toronto Maple Leafs and other teams. Daniel became a vegetarian in 2000 and has been vegan since 2006.[10] After many years living in the United States, he received his green card on July 15, 2009. On November 23, 2009, his mother died in her sleep after being ill for many months.[11]

Negreanu has a history of philanthropy. In addition to frequent appearances in charity events such as "Ante Up for Africa", which raises money for the crisis-torn region of Darfur, Negreanu is the founder of the annual "Big Swing" charity golf event.[12] The first annual Big Swing event was held on June 25 2009 at the Harrah’s Rio Secco Golf Club. Professional poker players paired with celebrities who donated $3,000 to the Lili Claire Foundation. The Lili Claire Foundation is a Las Vegas charity that serves children born with special needs and their families.[13]

Negreanu is an accomplished tournament and cash game player. He has amassed six World Series of Poker (WSOP) and two World Poker Tour (WPT) championships, reached numerous WSOP and WPT final tables, and won various other tournament titles. Negreanu's most successful year was 2004, when he was named the Card Player Player of the Year[14] and the WSOP Player of the Year.[15] He was also named the 2004-05 WPT Player of the Year.[16] In 2006, Negreanu was named "Favorite Poker Player" at Card Player Magazine's Player of the Year Awards Gala. In 2013, he captured two WSOP bracelets as well as another WSOP Player of the Year award, becoming the only player who wins this award twice.[17] In November 2014, Negreanu was inducted into the 'Poker Hall Of Fame' in Las Vegas.

In the past, Negreanu has regularly played the "Big Game" in Bobby's Room, in the Bellagio casino, Las Vegas, where the limits are $400–$800 or greater and the games are mixed. He is a self-admitted action junkie who always seeks new challenges and sets high goals for himself, not only at the poker table but also on the golf course. Unlike many other players, he is very outspoken about his poker results and regularly posts updates in the forums at the Full Contact Poker website. Some of Negreanu’s success is attributed to his ability to read opponents. When asked about this, Negreanu explained that the most important skill he employs is observing what hands his opponents play and how capable they are of playing them.[18]

Negreanu appeared on the tournament poker scene in 1997 with three tournament wins, including two events at the World Poker Finals at Foxwoods, earning $55,064 and being named the tournament's best all-around player.

As of 2015, his total live tournament winnings exceed $29,825,000.[19] His 78 cashes at the WSOP account for $14,641,383 of those winnings.[20] As of August 13, 2014, Negreanu was ranked #2 on the Global Poker Index.[21]

Negreanu's first in-the-money finish at the WSOP also happened to be his first WSOP bracelet. Negreanu won $169,460 in the $2,000 Pot Limit Hold'em event in the 1998 World Series of Poker, becoming the youngest WSOP bracelet winner in history — a record he held until 2004.[22] Negreanu has since captured another five bracelets. He has 31 career WSOP final table appearances, including two apiece at the WSOP Europe and at the WSOP Asia-Pacific, and 70 money finishes.[15]

In 1997, he won two events at the World Poker Finals at Foxwoods, earning $55,064 as well as being named the tournament's best all-around player.

In November 2008, Negreanu won the fourth-annual British Columbia Poker Championships main event, topping a field of 690 players (a personal high for Daniel), and earning $371,910 CAD ($299,951 USD).[23]

In addition to Negreanu's regular appearances in the big game at Bobby's Room, he played in seven seasons of the television show High Stakes Poker. He also played in two seasons of PokerStars Big Game.

In December 2005, Negreanu became the professional spokesperson for an online poker site called Poker Mountain. He promoted this site heavily on his official website Full Contact Poker (www.fullcontactpoker.com), which also includes his blog and a variety of poker forums. He played at this cardroom under the screen name "KidPoker". In June 2005 he announced his decision to terminate that relationship due to software issues that were problematic enough to cause a shutdown of the site.[24] In 2006, he used Full Contact Poker to launch a competition to select a protégé, whom Daniel would attempt to mold into a world-class live tournament poker player. He agreed to pay the protégé's entry fee into four $10,000 buy-in events. Daniel's first protégé was Brian Fidler. In 2007, Daniel ran a second protégé promotion, which was won by Anthony Mak. After "Black Friday" (the 2011 US government crackdown on online poker), Negreanu moved back to Canada in order to continue playing online poker on Poker Stars.

In June 2007, Negreanu signed with PokerStars, joining Chris Moneymaker, Joe Hachem, Greg Raymer and many other professional poker players as a member of Team PokerStars.[25] His Full Contact Poker site has since returned to being a forum and informational site.

Upon opening, the Wynn Las Vegas resort recruited him as their "Poker Ambassador" to play for any stake in their poker room. The arrangement lasted until October 2005, when he opted out because it was restricting his ability to play for high stakes outside the Wynn.